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Topic: Speed Measurement 0 to 12 km/h (Read 528 times) previous topic - next topic

John_Chappell

Ardunio Uno
I wish to measure the time in milliseconds between the operation of 2 reed switches [ 100 mm apart] when they open ( not close ) as there is very little bounce then.
Do I use unsigned long millis() to measure the time between SW1 & sw2 .
Or is there a way to use interupts?
I would be grateful for any help as this is my first project with a uno.
Regards, John Chappell

jremington

The basic idea is fine. You could use the two external interrupts, but it would probably work very well just to poll two inputs. 12 km/h is 3.3 m/s, so the shortest time between switch openings is about 100 milliseconds (a long time for the Arduino).

How do you plan to hold the switches closed, and what opens them?

John_Chappell

Hi JR,
A magnet keeps the reed sw closed and the rim of a steam loco interupts the magnetic field. IE to measure speed of train.

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